Sea creature some sailor caught (4)
I believe the answer is:
orca
'sea creature' is the definition.
(term for a killer whale)
'some sailor caught' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ORCA' can be found hidden inside 'sailor caught'.
(Other definitions for orca that I've seen before include "27 [WHALE]" , "Killer at sea" , "grampus" , "Large predator" , "Killer in deep" .)